Torsional rate sensor with momentum balance and mode decoupling

ABSTRACT

Rate sensor having a plurality of generally planar masses, a drive axis in the planes of the masses, an input axis perpendicular to the drive axis, and sense axes perpendicular to the drive axis and the input axis. The masses are driven to oscillate about drive axes and are mounted for torsional movement about the sense axes in response to Coriolis forces produced by rotation of the messes about the input axis, with sensors responsive to the torsional movement about the sense axis for monitoring rate of rotation.

BACKGROUND OF THE INVENTION

1. Field of Invention

This invention pertains generally to angular rate sensors or gyroscopesand, more particularly, to a dual mass rate sensor in which the massesare structurally constrained to oscillate in an anti-phase manner inboth drive and sense modes, momentum is balanced, and the drive andsense modes are decoupled.

2. Related Art

In rate sensors or gyroscopes, the use of two coupled proof masses whichoscillate in an out-of-phase manner in the drive mode is a common way ofbalancing the drive momentum in order to minimize the transfer of energyto the substrate. In addition, with the masses being driven in ananti-phase manner, the response of the masses to Coriolis forces willalso be out of phase, which allows the effects of external vibrations tobe cancelled.

Out-of-phase oscillation in the drive mode is commonly achieved bycoupling the two proof masses together with a spring, which has somesignificant disadvantages. The resulting dynamic system has tworesonances—a parasitic in-phase mode and the desired out-of-phase mode,with the in-phase mode always being lower in frequency than theout-of-phase mode. In addition, imperfections in fabrication oftenresult in the masses being of slightly different size, which preventsthem from oscillating with equal amplitudes. The unequal oscillationsproduce an imbalance in momentum and result in undesired transfer ofenergy to the substrate.

OBJECTS AND SUMMARY OF THE INVENTION

It is in general an object of the invention to provide a new andimproved angular rate sensor or gyroscope.

Another object of the invention is to provide a rate sensor or gyroscopeof the above character which overcomes the limitations and disadvantagesof rate sensors of the prior art.

These and other objects are achieved in accordance with the invention byproviding a rate sensor comprising two generally planar proof masses,means for driving the masses to oscillate in phase opposition aboutparallel drive axes in the planes of the masses, an input axisperpendicular to the drive axes, sense axes perpendicular to the driveaxes and the input axis, means mounting the masses for torsionalmovement about the sense axes in response to Coriolis forces produced byrotation of the masses about the input axis, means constraining the twomasses for anti-phase movement about both the drive axes and the senseaxes, sensing frames coupled to the masses for movement in response tothe torsional movement of the masses about the sense axes, and meansresponsive to movement of the sensing frames for monitoring rate ofrotation about the input axis.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a top plan view of one embodiment of a rate sensorincorporating the invention.

FIG. 2 is a top plan view of another embodiment of a rate sensorincorporating the invention.

FIGS. 2A and 2B are enlarged fragmentary top plan views of portions ofthe rate sensor in the embodiment of FIG. 2.

FIG. 3 is a fragmentary top plan view of another embodiment of a ratesensor incorporating the invention.

FIGS. 4 and 5 are top plan views of additional embodiments of a ratesensor incorporating the invention.

FIG. 6 is a fragmentary top plan view of another embodiment of a ratesensor incorporating the invention.

FIGS. 7-17 are top plan views of additional embodiments of a rate sensorincorporating the invention.

DETAILED DESCRIPTION

As illustrated in FIG. 1, the rate sensor has a pair of generally planarproof masses 11, 12 which lie in an x, y reference plane when the deviceis at rest. The input axis, i.e. the axis about which angular rate ofrotation is measured, is the y-axis, and the proof masses are disposedside-by-side along that axis for torsional movement about a pair ofdrive axes 13, 14 which extend in a direction parallel to the x axis.The proof masses are driven in an anti-phase manner for out-of-phasemovement through the reference plane as they pivot about the drive axes,with the inner edges 16, 17 of the two masses moving together in onedirection and the outer edges 18, 19 moving together in the oppositedirection.

The proof masses are also mounted for torsional movement about a pair ofsense axes 21, 22 which extend in the z-direction, perpendicular to thex, y plane and the other axes. Coriolis forces produced by rotation ofthe sensor about the y-axis cause the masses to rotate about the senseaxes, and since the masses are driven in an out-of-phase manner, theyrotate about the sense axes in opposite directions, with inner edges 16,17 again moving together in one direction and the outer edges 18, 19moving together in the other.

The midpoints of the inner or adjacent edges of the two proof masses areconnected together by a coupling link 24 which has a large out-of-planestiffness. Thus, the proof masses are constrained to oscillate about thedrive axes precisely out-of-phase and with exactly the same amplitude,thereby assuring that the angular momentum is perfectly balanced. Inaddition, the lowest mode of the overall system automatically becomesthe anti-phase drive mode. This cannot be achieved in any previouslyknown coupled mass system.

The coupling link also ensures that the sense mode responses of theproof masses are precisely out-of-phase and equal in amplitude,independent of the operating frequency.

In the embodiment of FIG. 1, each of the proof masses is mounted on apair of gimbals 26 for the torsional movement about the drive and senseaxes. The gimbals are pivotally mounted to anchors 28 by narrow flexures27 which are aligned with drive axes 13, 14 and permit torsionalmovement of the gimbals about the drive axes. The proof masses aresuspended from the gimbals by flexures 29 which permit torsionalmovement of the masses about the sense axes. In the embodimentillustrated, flexures 29 are located at the corners of the masses andextend in a diagonal direction, i.e. at an angle of 45 degrees to the xand y axes.

A sensing frame 31 surrounds the proof masses in the x, y plane and issuspended from anchors 28 by folded flexures 32 for linear movement inthe x-direction. Flexures 32 are flexible in the x-direction butrelatively stiff in the y and z directions so as to constrain the framefor movement in the x-direction only.

Links 33 are connected between the midpoints of the outer edges of theproof masses and the sensing frame for transforming torsional movementof the proof masses about the sense axes into linear movement of thesensing frame along the x-axis. Those links are connected to the frameby folded flexures 34 which are flexible in the y-direction andrelatively stiff in the x-direction. They allow out-of-plane deflectionsof the proof masses in the drive mode while transferring sense moderesponses to the sensing frame.

The position of the sensing frame and hence the torsional response ofthe proof masses is monitored by capacitors 36, 37 with electrode plates38 which are affixed to the frame and interleaved with stationary plates39 which are affixed to anchors 41. The capacitors are positioned onopposite sides of the frame and therefore react differentially tomovement of the frame.

In this embodiment, the gimbals 26 deflect only in the out-of-planetorsional drive direction, whereas the linear springs or flexures 29that suspend the proof masses from the gimbals allow the proof masses tooscillate only in the in-plane torsional sense mode relative to thegimbals. Thus, the suspension members utilized in the drive and sensemodes are independent of each other, which minimizes undesired dynamiccoupling between the two modes and suppresses the quadrature error andbias that result from such coupling.

Furthermore, the folded springs or flexures 32 which suspend the sensingframe 31 maintain it in perfect alignment with the sense direction.

Since the drive and sense mode responses of the proof masses aretorsional, any external linear acceleration results in zero displacementof the proof masses. However since linear sense mode deflection ofsensing frame 31 is coupled to the torsional sense mode response of theproof masses, the sensing frame deflects with linear acceleration in thex-direction.

In the sense mode, however, coupling link 24 and frame 31 deflect inopposite directions, with one being connected to the inner edges and theother being connected to the outer edges of the rotating proof masses.Hence, the net effect of the linear external acceleration can beexpressed ask _(x) x=a _(x)(m _(F) −m _(C)).

By making the mass of the frame (including links 33 and flexures 34)equal to the mass of coupling link 24, the effect of any linear orangular acceleration can be nulled out, and susceptibility of the deviceto vibration is minimized.

Similarly, the device can be adapted for simultaneous detection ofangular rate and linear acceleration by making the mass of the framemuch greater than the mass of the coupling link. In that case, anylinear acceleration along the deflection axis of the sensing frame canbe detected by low-pass filtering of the output signals beforedemodulating them to extract the Coriolis signals.

The drive and sense modes can also be decoupled by suspending the proofmasses from a structure that deflects only in the in-plane torsionalsense mode, with the proof masses deflecting only in the torsionalout-of-plane drive mode with respect to the supporting structure and thein-plane deflections of the supporting structure being coupled to thesensing frame. Such an embodiment is shown in FIG. 2.

In this embodiment, proof masses 42, 43 are pivotally mounted on gimbals44 by flexures 46 which permit out-of-plane torsional movement of themasses about drive axes 13, 14. The gimbals are suspended from anchors47, 48 by flexures 49 for in-plane torsional movement about sense axes21, 22. As best seen in FIG. 2A, the midpoints of the inner or adjacentedges of the proof masses are connected together by a coupling link 51consisting of thin flexures 52 which extend in the x-direction. Thus,the inner portions of the masses are tied together for movement inconcert both in the out-of-plane drive mode and in the in-plane sensemode, as in the embodiment of FIG. 1. The gimbals which support the twomasses are connected together by flexures 53 in the region between theadjacent edges of the masses.

Sensing beams or frames 56 extend in a direction parallel to the inputor y-axis on opposite sides of the masses and are suspended from anchors48 by flexures 57 for linear movement along the drive axes. The ends ofthe sensing frames are connected to the outer edges of the proof massesby links 58. Linear movement of the sensing frames and, hence, thein-plane sense mode torsional movement of the proof masses is monitoredby capacitors 59 consisting of plates 61 connected to the frames andstationary plates 62 connected to anchors 63.

As in the embodiment of FIG. 1, the proof masses are driven in ananti-phase manner, and Coriolis forces produced by rotation about theinput axis cause the masses to oscillate in opposite directions aboutthe sense axes, with the inner edges of the masses moving in onedirection and the outer edges moving in the other. This torsionalmovement is converted to linear movement of the sensing frames andmonitored by capacitors 59.

The embodiment of FIG. 3 is similar to the embodiment of FIG. 2, withthe addition of diagonally extending flexures 66 at the corners of thegimbals. The additional flexures provide increased stiffness in the xand y directions and significantly reduce the susceptibility of thesensor to vibration. In this embodiment, the portions of the gimbals 44a between the proof masses serve as counterbalances, and thesusceptibility to vibration can be reduced to zero by increasing themass of these counterbalances.

The embodiments of FIGS. 4 and 5 are similar to the embodiment of FIG.3, and like reference numerals designate corresponding elements in allthree of them. In the embodiment of FIG. 4, however, the arms 44 a ofthe gimbals which serve as a counterbalance are made equal in mass tosensing frames 56 so the inertial force on the frame due to linearacceleration is nulled out by the inertial force on the counterbalance.In addition, each of the sensing frames is suspended from anchors 48 bya two pairs of flexures 57 instead of just one, which further stabilizesthe device.

The embodiment of FIG. 5 is designed for simultaneous detection ofangular rate and linear acceleration. In this embodiment, the mass ofsensing frames 56 is made substantially larger than the mass of thecounterbalance arms 44 a, and the counterbalance mass is thuseliminated. The deflection due to linear acceleration along thedeflection axis of the sensing frames is maximized and detected by lowpass filtering of the output signals from capacitors 59 beforedemodulating those signals to extract the Coriolis signal.

In the embodiment of FIG. 6, gimbals 68 are suspended by flexures 69from anchors 71 which are located inboard or toward the centers of proofmasses 72, 73. The flexures extend diagonally from the four corners ofeach of the proof masses and permit the torsional in-plane oscillationof the proof masses and gimbal in the sense mode. Having the anchorslocated close to the centers of the masses minimizes the effects ofstress on the packaging of the sensor. If desired, the four flexures canbe suspended from a single, centrally located anchor instead of the fourseparate anchors shown in this embodiment.

As in the previous embodiments, the proof masses are connected to thegimbals by flexures 74 for out-of-plane oscillation about the drive axesin the drive mode. The midpoints of the adjacent edges of the proofmasses are connected together by a coupling 76, and the arms of thegimbals between the masses are connected together by flexures 77.

Sensing beams or frames 79 are suspended from anchors 81 by foldedflexures 82 which constrain the frames for linear movement in thex-direction. The midpoints of the outer arms of the gimbals areconnected to the frames by links 83 to transform sense mode oscillationsof the proof masses and gimbals into linear motion of the frames. Thoseoscillations are monitored by capacitors 84 with interleaved plates 86connected to the sensing frames and to anchors 87.

Finite element analysis of the embodiment shown in FIG. 6 shows that thefirst resonance mode of the structure is the anti-phase drive mode andthat the second mode is the sense mode. The lowest unwanted resonancemode was also observed to be over 5 KHz higher than the sense mode,providing the desired separation of the unwanted modes from theoperational modes. This mode separation cannot be achieved with anyother known mechanically coupled system with two degrees of freedom.

The embodiment of FIG. 7 is generally similar to the embodiment of FIG.6, with gimbals 68 suspended by flexures 69 from inboard anchors 71 fortorsional in-plane oscillation in the sense mode, proof masses 72, 73connected to the gimbals by flexures 74 for out-of-plane oscillationabout the drive axes in the drive mode, and the midpoints of theadjacent edges of the proof masses connected together by a coupling 76for movement in concert.

In this embodiment, however, the detection frame is divided into foursections 91-94 which are suspended from anchors 96, 97 by foldedflexures or springs 98 for movement independently of each other in thesensing (y) direction.

The midpoints of the side arms of the gimbals are connected to theframes by links 99 to transform torsional sense mode oscillations of theproof masses and gimbals about the z-axes into linear displacement ofthe frames. Those displacements are monitored by capacitors 101A-101Dhaving interleaved plates 102, 103 connected to the sensing frames andto anchors 104.

As in the other embodiments, masses 72, 73 are driven to oscillate insee-saw fashion about the x-axes, and rotation about the y-axis causesthe masses to oscillate about the z-axes, with the rotation about thez-axes being converted to linear movement of sensing frames 91-94. Inthis embodiment, however, the capacitor electrodes or plates extend inthe x-direction, and the sensing frames move in the y-direction.

The flexures are orders of magnitude stiffer in all directions otherthan the sensing direction, which minimizes the motion of the sensingelectrodes due to the drive motion and to any other spurious motion ofthe structure. It also provides better decoupling of the drive mode fromthe sense mode and minimizes quadrature error.

A significant advantage of the split frames is the ability to rejectexternal accelerations as common mode by employing double differentialdetection, e.g. (C_(A)+C_(C))−(C_(B)+C_(D)), where C_(A), C_(B), C_(C)and C_(D) are the capacitances of capacitors 101A-101D. The split framesalso minimize the total additional inertia of the detection frame.

In the embodiment of FIG. 8, inner sensing frames 106 are suspended fromanchors 107 by diagonally extending flexures 108 and thereby constrainedfor torsional movement only in the x, y plane. These frames arepositioned within windows 109 a, 111 a in proof masses 109, 111, withthe proof masses being suspended from the frames by torsional hinges 112which permit the masses to pivot in see-saw fashion about x-axes in thedrive mode but transmit sense mode motion about the z-axes to theframes.

The adjacent edges of the proof masses are connected together by acoupling 113 for movement in concert both in the z-direction in thedrive mode and in the x-direction in the sense mode.

This embodiment also has four outer sensing frame sections 114 which aresuspended from anchors 116 by a combination of flexures 117 and foldedflexures 118 for rotational movement about z-axes. The outer framesections are connected to inner sensing frames 106 by links 119 so thatthe outer sections rotate in concert with the inner frames. Rotation ofthe sensing frames is monitored by capacitors 121 which have interleavedplates 122, 123 connected to the outer sensing frames and to anchors124.

In the drive mode, masses 109, 111 are driven out-of-phase and pivot insee-saw fashion about the x-axes. Rotation about the y-axis producesCoriolis forces which cause the masses to rotate in opposite directionsabout the z-axes. The rotation of the masses is transferred to innersensing frames 106 by hinges 112 and then to outer frames 114 by links119. The sensing capacitors at the ends of the outer frames are drivendifferentially, with the plates moving closer together at one end ofeach frame and farther apart at the other.

Having substantial portions of the sensing frames inside the proofmasses minimizes the inertia of the sense mode, and the modes areeffectively decoupled since the inner sense mode frames are free tooscillate only in the torsional sense mode and are strictly constrainedin all other modes of motion.

The torsional hinges which connect the proof masses to the inner framesallow the masses to move relative to the frames in the drive mode whiletransmitting the sense mode responses of the masses to the sensingframes. Transmitting the sense mode oscillation of the inner frames toouter frames which carry the sensing electrodes provides differentialtorsional detection which enhances immunity to both linear vibration andangular vibration.

In the embodiment of FIG. 9, the sensing frames 126 are located entirelywithin windows 127 a, 128 a in proof masses 127, 128. As in theembodiment of FIG. 8, the sensing frames are suspended from centralanchors 129 by flexures 131, and the proof masses are suspended from thesensing frames by torsion springs 132 which permit the masses to pivotin see-saw fashion about the x-axes, but transfer sense mode rotationabout the z-axes from the masses to the frames.

The adjacent edges of the proof masses are connected together by acoupling 133 for movement in concert both in the z-direction in thedrive mode and in the x-direction in the sense mode.

Rotation of the sensing frames is monitored by capacitors 134 which arealso located entirely within the proof masses. These capacitors haveelectrodes or plates 136 which are attached directly to the sensingframes and interleaved with stationary electrodes or plates 137 affixedto anchors 138.

In operation, proof masses 127, 128 are driven to oscillate in ananti-phase manner about the x-axes, and the Coriolis forces produced byrotation about the y-axis cause the masses to rotate about the z-axes.This rotation is transferred to sensing frames 126 to move plates 136and produce a change in the capacitance of sensing capacitors 134.

Having the capacitor plates attached directly to the sensing frame, withboth the plates and the frame being positioned entirely within themasses permits the device to be constructed in compact form withessentially perfect symmetry, which makes this embodiment even moreimmune to linear and angular vibration than the embodiment of FIG. 8.

In the embodiment of FIG. 10, proof masses 139, 141 are mounted onframes 142 for rotation about the y-axis in the drive mode and thez-axis in the sense mode. The frames are mounted to the substrate bytorsion springs 143 which extend in the y-direction and permit theframes to pivot in see-saw fashion about the y-axis, with the massesbeing connected to the frames by flexures or springs 144 which extend inthe x-direction. The drive and sense modes of the masses are thusdecoupled, with the drive mode frequency (rotation about the y-axis)being dominated by torsion springs 143 and the detection mode frequency(rotation about the z-axis) being determined primarily by the bending ofsprings 144.

Masses 139, 141 are identical, and frames 142 are positioned centrallyof the masses, with the y- and z-axes of rotation passing through thephysical centers of the masses.

Each of the masses is driven by an electrode (not shown) positionedbeneath it for rotation about the y-axis in an anti-phase manner. Thetwo masses are coupled together at the midpoints of their adjacent edgesby a coupling spring 146 which permits the masses to be driven either inphase or out of phase. The spring separates the anti-phase drive modefrom the in-phase mode, with the anti-phase frequency increasing withthe stiffness of the spring, while the in-phase mode frequency remainsthe same. The coupling spring also constrains the two masses forrotation together about the z-axis so that when one mass rotates in onesense, the other must rotate in the opposite sense, thereby ensuringanti-phase proof mass motion in the detection mode.

Detection, or sensing, frames 148 are mounted to the substrate byflexures 149, 151 for rotation about the z-axis. These frames arecoupled to the proof masses by link springs 152, which transferrotational movement about the z-axes from the masses to the frames. Suchrotation is monitored by capacitors 153 which have plates 154 attachedto the frames and interleaved with stationary plates 156 affixed toanchors 157 on the substrate. These capacitors also provide feedback forforce rebalancing.

Link springs 152 extend in the y-direction and are preferably madetorsionally weak in order to minimize coupling between the drive modeoscillation of the masses and the detection frames. Such coupling couldresult in a slight vertical vibration of the capacitor plates carried bythe frames which could detract from the performance of the sensor. Atthe same time, however, the springs should not be made so weak that thetransfer of z-axis rotation is degraded.

To enhance immunity to angular vibration noise, coupling springs 159 areconnected between the confronting arms of the detection frames. Thesesprings are relatively soft in the y-direction and stiff in thex-direction in order to enhance coupling and ensure that the framesoscillate in a true anti-phase manner.

In operation, proof masses 139, 141 are driven to oscillate out-of-phasewith each other in see-saw fashion about the y-axis, and rotation of thesensor about the x-axis results in out-of-phase Coriolis inducedrotation of the masses about the z-axes. That rotation is transferred todetection frames 148 by link springs 152, with the rotation of each ofthe frames being opposite to that of the adjacent proof mass. Thus, forexample, when mass 139 rotates in a clockwise direction about thez-axis, the upper link spring 152 forces the upper detection arm torotate in a counter-clockwise direction about its z-axis. At the sametime, mass 141 rotates in a counter-clockwise direction, and the lowerdetection frame rotates in a clockwise direction.

Having the two detection frames rotate in opposite directions provides asignificant advantage in reducing the sensitivity of the device tovibration noise and angular acceleration about the z-axis.

The embodiment of FIG. 11 is similar to that of FIG. 10 in that proofmasses 161, 162 are mounted on frames 163 for rotation about the y-axisin the drive mode and the z-axis in the sense mode. The frames aremounted to anchors 164 on the substrate by flexures or torsion springs166 which extend in the x-direction, and the masses are connected to theframes by flexures or torsion springs 167 which extend in they-direction.

As in the previous embodiments, the two masses are coupled together atthe midpoints of their adjacent edges by a coupling spring 168. Thisspring is in the form of a small rectangular frame, with relativelylong, flexible flexures extending in the x-direction and relativelyshort, stiff ones in the y-direction. This design decouples thetorsional stiffness of the spring about the y-axis for drive from thelinear stiffness along the x-axis for detection while permitting the twomasses to be driven either in an in-phase manner or in an anti-phasemanner.

Detection, or sensing, frames 169 are coupled to the proof masses bylink springs 170. These frames are similar to frames 148 in theembodiment of FIG. 10, although they are perforated to reduce the massof the detectors. The frames are mounted to the substrate by flexures171, 172 for rotation about z-axes, and the rotation of the frames, andhence the masses, is monitored by capacitors 173 which are similar tocapacitors 153.

Coupling springs 174 are connected between the confronting arms of thedetection frames. These springs are similar to coupling springs 159 inthe embodiment of FIG. 10 in that they are relatively soft in they-direction and stiff in the x-direction in order to enhance couplingand ensure that the frames oscillate in a true anti-phase manner.However, they are simpler than springs 159 in that they have only twoleaves instead of four.

Operation and use of the embodiment of FIG. 11 is similar to that of theembodiment of FIG. 10, with coupling springs 168, and link springs 170providing both good coupling of z-axis rotation between the proof massesand the detection frames in the sense mode and good isolation betweenthe masses and the frames for y-axis rotation in the drive mode.

In the embodiment of FIG. 12, detection frames 176 and sensingcapacitors 177 are located entirely within proof masses 178, 179, andthe detection frames and the masses are symmetrical about the x- andy-axes and have the same centers of rotation in the sense mode. Thiseffectively prevents rotational responses about the z-axis from beinginduced by linear acceleration along the x-axis because the detectorsare inertially balanced along the x-axis with regard to their centers ofrotation. Also, since the masses and the detectors have the same centersof rotation, there is no tendency to produce rotation about the z-axisas can happen when the rotation centers are separated and the lineardisplacements produced by linear acceleration along the x-axis aredifferent.

Frames 176 are mounted to anchors 181 by flexures or springs 182, 183which extend along the x- and y-axes that intersect at the centers ofthe masses and the frames. Each of the masses is connected to one of theframes by a pair of torsion springs 184 which extend along the y-axis,and the two masses are coupled together at the midpoints of theiradjacent edges by a coupling spring 186 which is similar to spring 168in the embodiment of FIG. 10. Since torsion springs 184 determine thein-phase drive mode frequency, they are normally made much stiffer thanlink springs 152 in the embodiment of FIG. 10.

Capacitors 177 have plates 187 which extend from frames 176 and areinterleaved with stationary plates 188 attached to anchors 189, 191.

In this embodiment, proof masses 178, 179 are once again driven tooscillate in an anti-phase see-saw fashion about the y-axis, androtation about the x-axis is sensed. The Coriolis forces produced bythat rotation cause the masses to rotate in opposite directions aboutthe z-axes which pass through the centers of the masses. The z-axisrotation is transferred to detection frames 176 by torsion springs 184,and the frames rotate in the same direction as the masses and about thesame centers of rotation as the masses. As noted above, since the proofmasses and the detectors are symmetrical about the x- and y-axes andhave the same centers of rotation, this embodiment is substantiallyimmune to linear acceleration along the x-axis.

In the embodiment of FIG. 13, the rate sensor has two proof masses 193,194 in the x-y plane, with mass 193 being positioned inside mass 194.Each mass is mounted to the substrate through a pair of torsion springs196 attached to anchors 197 for rotation about the y-axis. Thus, insteadof having spaced apart drive axes as in some of the other embodiments,these masses have coincident drive axes.

The ends of the masses are connected to a pair of coupling frames 198 bytorsion springs 199, and each of the coupling frames is mounted on adetection frame 201 by additional torsion springs 202 which allow thecoupling frames to rotate about the y-axis. The two masses are thuscoupled together and constrained for rotation with equal amplitude inopposite directions. By proper design of the masses, the linear andangular momentum of the drive motion can be balanced.

Detection frames 201 are mounted on the substrate by flexures or springs203 which are attached to anchors 204 at the centers of the frames forrotation about the z-axis.

In the presence of input rotation about the x-axis, the anti-phase drivemotion generates Coriolis forces that cause masses 193, 194 to rotateabout the z-axis in an anti-phase manner. This motion is transferred todetection frames 201 through coupling frames 198, resulting in in-phaserotational motion of the detection frames about the z-axes, with thecoupling frames constraining the detection frames to rotate at the sameamplitude and in the same direction about the z-axes, independent offrequency. The response to the rotation about the x-axis is monitored bycapacitors 206 with plates 207 attached to the detection frames andstatic plates 208 on the substrate.

In this embodiment, the symmetry of both the drive elements and thedetection elements provides for momentum balance, immunity to linearvibration excitation, and reduced susceptibility of these properties tovariations in the fabrication process. The use of mechanical constraintrather than coupling springs enables the drive and detection modes to bethe lowest frequency modes of the system. Also, since the proof massesare mounted to the substrate through their own anchors and connect tothe detection frames through torsion springs, these springs can be mademuch weaker than the springs which mount the masses, thereby minimizingthe leakage of driving motion into the detection frames, quadratureerror, and other spurious error signals. The weaker coupling springsalso minimize the inertia forces induced on the detection frames by themasses due to externally applied accelerations.

The embodiment of FIG. 14 has a proof mass 211 and a pair of couplingframes 212 which also serve as proof masses. Mass 211 is mounted on aframe 213 which is mounted to anchors 214 by springs or flexures 216,217 for rotation about the z-axis at the center of the mass, and it isconnected to the frame by torsion springs 218 for rotation about they-axis. Mass 211 is connected to coupling frames 212 by torsion springs219 which are similar to torsion springs 199 in the embodiment of FIG.13.

Torsion springs 220 connect coupling frames 212 to detection frames 221which are constrained for rotation about z-axes by flexures 222, 223connected to anchors 224, 226. The coupling frames are generallyU-shaped and extend along three sides of the detection frames. Rotationof the detection frames is monitored by capacitors 227 which haveelectrodes or plates 228 attached to the frames and stationaryelectrodes or plates 229 affixed to anchors 231. The open sides of thedetection frames simplify fabrication of the device in that they permitthe electrodes to be routed out from the side without the need forbackside vias through the substrate.

In operation, proof mass 211 and coupling frames 212 are driven tooscillate in see-saw fashion about y-axes, with the coupling framesbeing out of phase with the proof mass and in phase with each other.Coriolis forces produced by rotation about the x-axis cause the proofmass and the coupling frames to rotate about z-axes, with the framesonce again in phase with each other and out of phase with the proofmass. The z-axis rotation of the coupling frames is transferred todetection frames 221 by torsion springs 220.

Since the rotation of coupling frames 212 is opposite to that of proofmass 211 in the drive mode, the drive momentum can be balancedrelatively easily by proper design of these masses, as can inertiabalance in the detection mode for the rejection of angular vibration. Inaddition, pivotally mounted frame 213 helps to decouple the out-of-planedrive motion of the proof mass from the rotational sense motion of thatmass and detection frames 212.

The embodiment of FIG. 15 has a central proof mass 233 which is mountedon a frame 234 for rotation about the y- and z-axes and a pair of outerproof masses 236 on opposite sides of the central mass. The frame ismounted to anchors 237, 238 by flexures 239, 241 for rotation about thez-axis at the center of mass 233, and the mass is connected to the frameby torsion springs 242 for rotation about the y-axis.

Each of the outer proof masses 236 is rotatively mounted on a detectionframe 244 by torsion springs 246 for rotation about the y-axis whichpasses through the center of the mass, and the detection frames aremounted to anchors 247, 248 by flexures or springs 249, 251 for rotationabout the z-axes at the centers of the masses. Flexures 251 extend inthe y-direction and are aligned along common axes with torsion springs246.

The outer edges of central proof mass 233 are connected to the adjacentedges of outer proof masses 236 by couplings 252 whereby the outermasses are constrained for out-of-phase movement relative to the centralmass and in-phase movement relative to each other about both the y- andz-axes.

Detection frames 244 are generally U-shaped and extend along three sidesof outer proof masses 236. Rotational movement of the proof masses aboutthe z-axes is monitored by capacitors 254, 256. Capacitors 254 haveelectrodes or plates 257 on the detection frames and interleaved withstationary electrodes or plates 258 affixed to anchors 259, with theplates extending in the y-direction and being spaced apart in thex-direction. Capacitors 256 have electrodes or plates 261 on thedetection frames and interleaved with stationary electrodes or plates262 affixed to anchors 263, with the plates extending in the x-directionand being spaced apart in the y-direction.

In the drive mode, central proof mass 233 is driven out of phase withouter proof masses 236 for oscillation about the respective y-axes.Rotation about the x-axis produces Coriolis forces which cause themasses to rotate about their z-axes, with the outer masses being out ofphase with the central mass and in phase with each other.

Outer masses 236 are symmetrical in shape, which provides morerobustness against process variations in maintaining momentum balance,and detection efficiency is increased by having detection frames 244outside those masses. In the sense mode, the rotation of the outermasses in phase with each other and in phase opposition to the centralmass produces a net cancellation of linear and angular momentum. Thetorsional springs and flexures provide a high level of decouplingbetween the drive and sense motions, and the symmetry of the sensormakes it insensitive to externally applied accelerations.

The embodiment of FIG. 16 is similar to the embodiment of FIG. 12, andlike reference numerals designate corresponding elements in the two. Inthe embodiment of FIG. 16, however, proof masses 178, 179 are suspendedfrom anchors 266 by drive springs consisting of torsion springs 267, 268and a rigid connecting bar 269. The drive springs have a generallyU-shaped configuration, with the two torsion springs being spaced apartand extending parallel to the y-axis and the bar extending between them.At the ends opposite the bars, springs 267 are connected to the anchors,and springs 268 are connected to the masses. Each of the masses issuspended by four of the drive springs which are disposed symmetricallyof the y-axis and the centers of the masses. These springs constrain themasses for see-saw movement about the y-axis and rotational movementabout the z-axes which pass through the centers of the masses.

The masses are connected to sensing frames 176 by link springs 271 whichare substantially weaker than springs 267, 268 in torsional stiffness.

In operation, proof masses 178, 179 are driven to oscillate in ananti-phase see-saw fashion about the y-axis, and rotation about thex-axis is sensed. The Coriolis forces produced by that rotation causethe masses to rotate in opposite directions about the z-axes which passthrough the centers of the masses. The z-axis rotation is transferred todetection frames 176 by link springs 271, and the frames rotate in thesame direction as the masses and about the same centers of rotation asthe masses. Since the proof masses and the detectors are symmetricalabout the x- and y-axes and have the same centers of rotation, thisembodiment is substantially immune to linear acceleration along thex-axis.

Moreover, with drive springs 267, 268 being much stiffer torsionallythan link springs 271, the drive springs dominate the in-phase drivemode frequency, and the transfer of angular momentum from the drive modeto the sensing frame is greatly reduced, resulting in significantly lessvertical motion of the sensing frame.

The embodiment of FIG. 17 is similar to the embodiment of FIG. 7 in thatgimbals 272 are suspended by diagonally extending flexures 273 frominboard anchors 274 for torsional in-plane oscillation in the sensemode. Proof masses 276, 277 are connected to the gimbals by torsionsprings 278 for out-of-plane oscillation about the drive axes in thedrive mode, and the midpoints of the adjacent edges of the proof massesconnected together for movement in concert by a coupling 279.

In this embodiment, however, the proof masses and gimbals are generallycircular, and the movable electrodes or plates 281, 282 of feedbackcapacitors 283 and sensing capacitors 284 are attached directly to thegimbals rather than to separate sensing frames. The fixed electrodes orplates 286, 287 of the capacitors are mounted in a stationary positionon frames 288, 289 attached to anchors 291, 292. The inner end portionsof the gimbals are connected together by couplings 293.

As in the embodiment of FIG. 7, the sensing capacitors are divided intofour separate sections, and a differential torsional detection schemecan be employed. That provides a significant improvement in immunity tolinear and angular vibration. Moreover, with the capacitor platesattached directly to the gimbals, the structure of this embodiment ismuch simpler than those which separate sensing frames.

In operation, masses 276, 277 are driven to oscillate in see-saw fashionabout the x-axes which pass through their centers, and rotation aboutthe y-axis causes the masses to oscillate about the z-axes which passthrough their centers. The rotation about the z-axes is transferred togimbals 272 by torsion springs 278 and monitored by capacitors 284. Withtheir inner edge portions coupled together, the two masses areconstrained for rotation in opposite directions, as are the two gimbals.

As in the embodiment of FIG. 7, the sensing capacitors are divided intofour separate sections, and a differential torsional detection schemecan be employed. That provides a significant improvement in immunity tolinear and angular vibration. Moreover, with the capacitor platesattached directly to the gimbals, the structure of this embodiment ismuch simpler than those which separate sensing frames.

It is apparent from the foregoing that a new and improved rate sensorhas been provided. While only certain presently preferred embodimentshave been described, as will be apparent to those familiar with the art,certain changes and modifications can be made without departing from thescope of the invention as defined by the following claims.

1. A rate sensor comprising two generally planar proof masses, means fordriving the masses to oscillate in phase opposition about parallel driveaxes in the planes of the masses, an input axis perpendicular to thedrive axes, sense axes perpendicular to the drive axes and the inputaxis, means mounting the masses for torsional movement about the senseaxes in response to Coriolis forces produced by rotation of the massesabout the input axis, means constraining the two masses for anti-phasemovement about both the drive axes and the sense axes, sensing framescoupled to the masses for movement in response to the torsional movementof the masses about the sense axes, and means responsive to movement ofthe sensing frames for monitoring rate of rotation about the input axis.2. The rate sensor of claim 1 wherein the means constraining the twomasses comprises a mechanical link between adjacent edges of the masses.3. The rate sensor of claim 1 wherein the means for monitoring the rateof rotation comprises capacitors having plates which move relative toother plates in response to the movement of the sensing frames.
 4. Therate sensor of claim 1 wherein the sensing frames are constrained forlinear movement in response to the torsional movement of the masses. 5.The rate sensor of claim 1 wherein the sensing frames are constrainedfor rotational movement in response to the torsional movement of themasses.
 6. A rate sensor comprising two generally planar proof massesmounted side-by-side for anti-phase torsional movement about a pair ofspaced apart drive axes, an input axis perpendicular to the drive axes,sense axes perpendicular to the drive axes and the input axis, meansmounting the masses for torsional movement about the sense axes inresponse to Coriolis forces produced by rotation of the masses about theinput axis, means connecting adjacent inner edge portions of the twomasses together for movement in concert about both the drive axes andthe sense axes, a sensing frame constrained (or linear movement, andlinks connecting the masses to the sensing frame for transformingtorsional motion of the masses about the sense axes to linear motion ofthe sensing frame.
 7. The rate sensor of claim 6 wherein the masses aremounted on gimbals which are rotatable about the drive axes, withflexures mounting the masses to the gimbals for torsional movement aboutthe sense axes.
 8. The rate sensor of claim 6 wherein the masses aremounted on gimbals for torsional movement about the drive axes, and thegimbals are mounted on flexures which permit torsional movement of thegimbals and the masses about the sense axes.
 9. The rate sensor of claim8 wherein the flexures are connected to anchors outside the masses. 10.The rate sensor of claim 8 wherein the flexures are connected to anchorsnear the centers of the masses.
 11. The rate sensor of claim 6 whereinthe means connecting the inner edge portions of the two masses togethercomprises a coupling link.
 12. The rate sensor of claim 11 wherein thesensing frame and the coupling link have equal masses and linearacceleration of the sensing frame and the coupling link in a directionparallel to the drive axes balance each other out.
 13. The rate sensorof claim 11 wherein the sensing frame has a greater mass than thecoupling link and the sensor is responsive to linear acceleration of thesensing frame in a direction parallel to the drive axes as well as torotation about the input axis.
 14. A rate sensor comprising twogenerally planar proof masses, a drive axis in the plane of each of themasses, means for driving the masses to oscillate in phase oppositionabout the drive axes, an input axis perpendicular to the drive axes,sense axes perpendicular to the drive axes and the input axis, meansmounting the masses for torsional movement about the sense axes inresponse to Coriolis forces produced by rotation of the masses about theinput axis, means constraining the two masses for anti-phase movementabout both the drive axes and the sense axes, a pair of sensing framescoupled to opposite sides of each of the masses for movement in oppositedirections in response to the torsional movement of the masses about thesense axes, and electrode plates on the sensing frames which move inopposite directions relative to fixed plates on the opposite sides ofthe masses to form capacitors which change value in opposite directionsin response to the torsional movement of the masses about the senseaxes.
 15. The rate sensor of claim 14 wherein the drive axes are spacedapart and parallel to each other.
 16. The rate sensor of claim 14wherein the sensing frames are constrained for movement in directionsperpendicular to the drive axes.
 17. The rate sensor of claim 14 whereinthe means mounting the masses comprises a pair of gimbals on which themasses are pivotally mounted for movement about the drive axes, andflexures mounting the gimbals for rotational movement about the senseaxes.
 18. The rate sensor of claim 17 wherein the flexures are connectedto anchors near the centers of the masses.
 19. A rate sensor comprisinga pair of spaced apart, parallel drive axes, an input axis perpendicularto the drive axes, sense axes perpendicular to the drive axes and theinput axis, a pair of generally planar proof masses pivotally mounted oninner frames for see-saw movement about the drive axes, with the innerframes being located entirely within the lateral confines of the massesand being mounted for rotational movement about the sense axes, sensingframes mounted on opposite sides of the masses for rotation about axesparallel to the sense axes, means for transferring rotational movementof the masses to the sensing frames, and electrode plates on the sensingframes which are interleaved with fixed plates to form capacitors whichchange in value in response to rotational movement of the masses aboutthe sensing axes.
 20. The rate sensor of claim 19 wherein the innerframes are mounted by flexures which extend from anchors at the centersof the masses.
 21. The rate sensor of claim 19 wherein the masses andthe inner frames are symmetrical about the drive axes and the inputaxes.
 22. The rate sensor of claim 19 including a mechanical linkconnecting adjacent edge portions of the masses together for movement inconcert about the drive axes and the sensing axes.
 23. A rate sensorcomprising a pair of spaced apart, parallel drive axes, an input axisperpendicular to the drive axes, sense axes perpendicular to the driveaxes and the input axis, a pair of generally planar proof massespivotally mounted on sensing frames for see-saw movement about the driveaxes, means mounting the sensing frames for rotational movement aboutthe sense axes, means for transferring rotational movement of the massesto the sensing frames, and electrode plates on the sensing frames whichare interleaved with fixed plates to form capacitors which change invalue in response to rotational movement of the masses about the sensingaxes, with both the sensing frames and the capacitors being locatedentirely within the lateral confines of the masses.
 24. The rate sensorof claim 23 wherein the sensing frames are mounted by flexures whichextend from anchors at the centers of the masses.
 25. The rate sensor ofclaim 23 wherein the masses and the inner frames are symmetrical aboutthe drive axes and the input axes.
 26. The rate sensor of claim 23including a mechanical link connecting adjacent edge portions of themasses together for movement in concert about the drive axes and thesensing axes.
 27. A rate sensor comprising a pair of generally planarproof masses pivotally mounted within generally circular gimbals forsee-saw movement about a pair of spaced apart, parallel drive axes, aninput axis perpendicular to the drive axes, sense axes perpendicular tothe drive axes and the input axis, means mounting the gimbals and themasses for torsional movement about the sense axes, and electrode platesextending radially from the gimbals interleaved with fixed electrodes toform capacitors which change in value in accordance with torsionalmovement of the masses about the sense axes in response to Coriolisforces produced by rotation of the masses about the input axis.
 28. Therate sensor of claim 27 wherein the sensing frames are mounted byflexures which extend outward from anchors near the centers of themasses.
 29. The rate sensor of claim 27 wherein the plates form separatecapacitors on opposite sides of the masses, and the values of thecapacitors on the opposite sides change in opposite directions.
 30. Therate sensor of claim 27 including a mechanical link connecting adjacentedge portions of the masses together for movement in concert about thedrive axes and the sensing axes.
 31. A rate sensor comprising twogenerally planar proof masses, means for driving the masses to oscillatein phase opposition about parallel drive axes in the planes of themasses, an input axis perpendicular to the drive axes, sense axesperpendicular to the drive axes and the input axis, means mounting themasses for torsional movement about the sense axes in response toCoriolis forces produced by rotation of the masses about the input axis,means constraining the two masses for anti-phase movement about both thedrive axes and the sense axes, and at least one sensing frame responsiveto the torsional movement of the masses about the sense axes.